Troubleshooting Connection Problems

Troubleshooting Connection Problems

A number of things can prevent a client application from successfully
connecting to Greenplum Database. This topic explains some of the common causes
of connection problems and how to correct them.

Table 1. Common connection problems

Problem

Solution

No pg_hba.conf entry for host or user

To enable Greenplum Database to accept remote client
connections, you must configure your Greenplum Database master instance
so that connections are allowed from the client hosts and database users that will be
connecting to Greenplum Database. This is done by adding the appropriate
entries to the pg_hba.conf configuration file (located in the
master instance's data directory). For more detailed information, see Allowing Connections to Greenplum Database.

Greenplum Database is not running

If the Greenplum Database master instance is down,
users will not be able to connect. You can verify that the Greenplum Database system is up by running the gpstate utility
on the Greenplum master host.

Network problems

Interconnect timeouts

If users connect to the Greenplum
master host from a remote client, network problems can prevent a connection (for
example, DNS host name resolution problems, the host system is down, and so on.). To
ensure that network problems are not the cause, connect to the Greenplum master host from the remote client host. For example:
ping hostname.

If the system cannot resolve the host names and IP
addresses of the hosts involved in Greenplum Database, queries and
connections will fail. For some operations, connections to the Greenplum Database master use localhost and others use the
actual host name, so you must be able to resolve both. If you encounter this error,
first make sure you can connect to each host in your Greenplum Database array from the master host over the network. In the /etc/hosts
file of the master and all segments, make sure you have the correct host names and
IP addresses for all hosts involved in the Greenplum Database array.
The 127.0.0.1 IP must resolve to localhost.

Too many clients already

By default, Greenplum Database is configured to
allow a maximum of 250 concurrent user connections on the master and 750 on a segment.
A connection attempt that causes that limit to be exceeded will be refused. This limit
is controlled by the max_connections parameter in the
postgresql.conf configuration file of the Greenplum Database master. If you change this setting for the master, you must
also make appropriate changes at the segments.